SBI 4U1
Genetics
Multiple Choice
Identify the letter of the choice that best completes the statement or answers the question.
____
____
1. The paired bases of a DNA molecule are best described as
A. covalently linked across the width of the double helix
B. identical
C. mirror images
D. complementary
E. single-stranded
2. The percentage composition of a nucleic acid molecule found in bacterial cells is
32.3% adenine
30.7% thymine
19.1% cytosine
17.9% guanine
____
3.
____
4.
____
5.
____
6.
____
7.
The molecule is most likely to be
A. double-stranded DNA.
D. double-stranded RNA.
B. mitochondrial DNA.
E. single-stranded DNA.
C. messenger RNA.
DNA replication
A. results in each cell produced by mitosis and cytokinesis having a complete set of genetic
instructions
B. causes cytokinesis to begin
C. occurs virtually all the time during the life of a cell
D. occurs during cytokinesis
E. has different characteristics in cells producing repair tissue and those producing growth
tissue
DNA replication
A. is the first step in protein synthesis
B. occurs in every living cell in a multicellular organism
C. occurs before cytokinesis
D. is only semi-conservative in eukaryotes, not prokaryotes
E. may be conservative or semi-conservative at different points in an organism's life-cycle
DNA is stable because hydrogen bonds are formed between
A. thymine and uracil
D. guanine and adenine
B. cytosine and thymine
E. purines and pyrimidines
C. adenine and uracil
The nucleotide at the end of one strand of a fragment of double-stranded DNA has a free phosphate attached
to the 5' carbon of its deoxyribose sugar. The complementary nucleotide has
A. a free phosphate attached to the 3' carbon of its deoxyribose sugar
B. a hydroxyl group (-OH) attached to the 3' carbon of its deoxyribose sugar
C. a free phosphate attached to the 5' carbon of its deoxyribose sugar
D. a hydroxyl group attached to the 5' carbon of its deoxyribose sugar
E. two hydrogen atoms attached to the 3' carbon of its deoxyribose sugar
The model for DNA structure proposed by Watson and Crick, by its very nature, suggests a way in which the
DNA molecule can replicate itself, because
A. each base is capable of specifying the base opposite to it in the double helix
B.
C.
D.
E.
____
8.
____
9.
____ 10.
____ 11.
____ 12.
____ 13.
the two strands are held together by hydrogen bonds
only four different bases are involved in the structure
hydrogen bonds only form when the strands are anti-parallel
each purine only forms hydrogen bonds with another purine and each pyrimidine only
forms hydrogen bonds with another pyrimidine
When DNA helicase is active, the result is
A. annealing of RNA primers to the DNA
B. formation of phosphodiester bonds
C. formation of hydrogen bonds
D. separation of the two strands of the double helix
E. swivelling of the single separated strands of DNA
During DNA replication, the function of RNA primers is to
A. open replication bubbles
B. serve as starting points for DNA strand elongation by DNA polymerase I in the 3' - 5'
direction
C. serve as starting points for DNA strand elongation by DNA polymerase III in prokaryotes
D. prevent new-separated strands of DNA from rejoining
E. serve as a binding site for DNA ligase
During DNA replication, one of the new strands of DNA is synthesized continuously, while the other is
synthesized as a number of separate fragments of DNA that are subsequently linked by DNA ligase. This is
because
A. replication starts at many points on the chromosome
B. RNA primers only anneal to one of the parental strands of DNA
C. DNA polymerase III only synthesizes DNA in the 3' - 5' direction
D. one of the parental strands is unwound slower than the other by helicase
E. DNA polymerase III only synthesizes DNA in the 5' - 3' direction
Which of the following statements concerning Griffith's work with Streptococcus pneumoniae is incorrect?
A. injected heat-killed S-form bacteria allowed mice to survive
B. injected heat-killed S-form bacteria together with live R-form bacteria killed mice
C. injected S-form bacteria killed mice
D. injected R-form bacteria killed mice
E. the S-form bacteria are enveloped with a capsule of polysaccharide
Hershey and Chase's experiment
A. was intended to demonstrate that the protein case of a bacteriophage remained outside a
bacterial cell after infection.
B. involved finding radioactivity inside bacteria infected with bacteriophage having DNA
labelled with 32P.
C. involved finding radioactivity inside bacteria infected with bacteriophage having DNA
labelled with 35S.
D. involved finding radioactivity inside bacteria infected with bacteriophage having protein
labelled with 32P.
E. involved finding radioactivity inside bacteria infected with bacteriophage having protein
labelled with 35S.
A DNA nucleotide contains
1. a cyclic nitrogen-containing part
2. a single ring containing five carbons
3. a part which contains four oxygen atoms surrounding a central atom.
In order, 1, 2 and 3 are
A. a base, a phosphate group, a sugar
D. a phosphate group, a sugar, a base
B. a sugar, a base, a phosphate group
E. a sugar, a phosphate group, a base
C. a base, a sugar, a phosphate group
____ 14. The main support to the DNA molecule is provided by two backbones which run along the two sides of the
double helix. These backbones consist of
A. sugars joined by ester links
B. phosphates joined by ester links
C. sugars and phosphates linked together
D. phosphates and bases linked together
E. sugars and bases linked together
____ 15. The following three activities were engaged in by three different scientists (or groups of scientists) who
helped to determine the nature of the hereditary material
1. transformation in bacteria
2. research to identify what part of a bacteriophage is injected into a host bacterial cell
3. X-ray diffraction analysis of the DNA molecule
____ 16.
____ 17.
____ 18.
____ 19.
____ 20.
The scientist(s) who engaged in these activities are, respectively,
A. Griffith, Franklin, Watson and Crick
B. Hammerling, Hershey and Chase, Watson and Crick
C. Watson and Crick, Hershey and Chase, Hammerling
D. Griffith, Hershey and Chase, Franklin
E. Griffith, Hammerling, Franklin
Cytokinesis is
A. the replication of DNA
B. the division of a eukaryotic nucleus into two daughter nuclei
C. the movement of chromatids along spindle fibres during anaphase
D. the division of the cytoplasm and organelles of a cell between two daughter nuclei
E. cell movement
In their experiment that showed that DNA replication in E. coli was semi-conservative, Meselson and Stahl
used
A. a radioactive isotope of nitrogen
B. nitrogen isotopes having different mass
C. ultraviolet light
D. radioactive phosphorus
E. nitrogen isotopes which had different numbers of protons
In what order do the following molecules become involved in DNA replication in E. coli?
1. single-stranded binding proteins
2. DNA polymerase III
3. primase
4. helicase
A. 4,1,3,2
D. 3,2,4,1
B. 4,3,1,2
E. 2,3,4,1
C. 1,3,4,2
An enzyme, which excises a mismatched base in a newly synthesized strand of DNA, is called
A. a primase
D. an exonuclease
B. a excisase
E. a gyrase
C. a polymerase
What was the role of Avery, McCarty and Macleod in developing an understanding of the role of DNA in
heredity?
A. They discovered transformation.
B.
C.
D.
E.
____ 21.
____ 22.
____ 23.
____ 24.
____ 25.
____ 26.
____ 27.
____ 28.
They demonstrated that the nucleus was necessary for cell regeneration.
They defined the dimensions of the DNA molecule.
They identified DNA as the agent responsible for transformation.
They identified the nature of the genetic material released by a bacteriophage into the cell
it is infecting.
Complementary base pairing is the result of
A. hydrogen bonding
B. the fact that complementary bases fit together physically
C. covalent bonding
D. ionic bonding
E. the fact that strands of DNA are wound around each other in a double helix
In DNA, phosphodiester bonds join
A. two phosphate groups
D. phosphate groups and bases
B. bases and sugars
E. two sugar molecules
C. phosphate groups and sugars
The arrangement of bases in a molecule of mRNA is best described as
A. branched
D. linked into a beta-pleated sheet
B. linear
E. circular
C. paired
Transcription of the lacZ and lacY genes of the lac operon begins when
A. lactose binds to the operator
B. RNA polymerase binds to the lacZ gene
C. the repressor protein binds to the inducer
D. the repressor is released from the promoter
E. lactose binds to RNA polymerase
The genetic code is
A. very similar in humans and apes, but different in horses
B. very similar in monkeys and rats, but different in starfish
C. very similar in camels and beetles, but different in a geranium
D. very similar in antelopes, pine trees, and blue-green algae
E. very similar in all eukaryotes, but different in prokaryotes
Which of the following correctly describes the order in which cell components become involved in protein
synthesis?
A. DNA polymerase, mRNA, ribosome, tRNA
B. mRNA, RNA polymerase, ribosome, tRNA
C. RNA polymerase, mRNA, tRNA, ribosome
D. RNA polymerase, mRNA, ribosome, tRNA
E. DNA, rRNA, tRNA, mRNA
The expression of the repressor (lacl) gene, which is part of the lac operon
A. occurs only when RNA polymerase binds to the promoter
B. causes lactose to pass through the cell membrane
C. occurs only when lactose is present
D. results in the removal of the repressor from the operator
E. is part of the negative control mechanism of the lacZ and lacY genes
DNA acts as a template for transcription. Which of the following statements regarding the DNA of a gene
being expressed is true?
A. After unwinding, both of the DNA strands act as templates.
B. After unwinding, only one of the DNA strands acts as a template.
C. The two strands only act as a template when paired.
D. In prokaryotes, the binding of RNA polymerase to unwound DNA occurs randomly on
either of the two strands.
E. The strand with the higher cytosine-guanine content acts as the template.
____ 29. Four genes (A,B,C,D) of a bacterium code for four enzymes (A,B,C,D), which act sequentially to catalyze the
production of compound D, as follows.
enzyme A
enzyme B
enzyme C
enzyme D
precursor  compound A  compound B  compound C  compound D
A number of mutant strains of the bacterium are isolated, which grow only on supplemented media, as
outlined below.
Medium supplemented with
compound A
compound B
compound C
compound D
strain 1
no growth
no growth
growth
growth
strain 2
no growth
growth
growth
growth
strain 3
no growth
no growth
no growth
growth
____ 30.
____ 31.
____ 32.
____ 33.
The mutations in strains 1, 2 and 3 (respectively) are in genes
A. C, B, D
D. B, A, C
B. C, B, A
E. A, B, C
C. D, C, A
A cell in cell culture is briefly immersed in radioactive uracil. After a short time, the radioactive uracil is
removed and the cell culture is washed with, and immersed in, nonradioactive uracil. Where would you
expect to find the main concentration of radioactive nucleic acid?
I. Immediately after immersion in the radioactive uracil solution.
II. Some time after the cell was returned to nonradioactive uracil.
A. in the nucleus in both cases
B. in the cytoplasm in both cases
C. I. in the nucleus; II. in the cytoplasm
D. I. in the nucleus; II. in the nucleus and cytoplasm
E. I. in the nucleus; II. outside the cell
The temperatures at which two segments of DNA unwind has been established. Segment A unwinds at 71.6
C, while segment B unwinds at 80.7 C. The difference is due to the fact that
A. A is more phosphorylated than B
B. B is richer in adenine-thymine pairs than A
C. B is richer in adenine-uracil pairs than A
D. B is richer in cytosine-guanine pairs than A
E. A is richer in adenine-cytosine pairings than B
In eukaryotes, introns are removed before mRNA leaves the nucleus because
A. they do not code for protein
B. they prevent the movement of ribosomes
C. they prevent the binding of ribosomes to mRNA
D. the mRNA would be too long to pass through the nuclear pores if the introns remained in
it
E. they do not consist of the same bases as the rest of the mRNA
Base pairing due to hydrogen bonding is fundamental to
A. the process of DNA transcription, but not to the process of DNA replication
B. the process of DNA replication. but not to the process of DNA transcription
C. neither process
D. both processes
____ 34.
____ 35.
____ 36.
____ 37.
____ 38.
____ 39.
____ 40.
E. mitosis, but not to DNA transcription
The splicing of the first-formed mRNA transcript by spliceosomes is necessary because
A. the poly-A tail must be added
B. introns need to be added
C. the poly-A tail and the cap must be removed
D. the transcript must be freed from the DNA
E. introns need to be removed
Suppose a tRNA molecule bearing the anticodon for cysteine, and with cysteine bound to it, is chemically
treated so as to change the cysteine to alanine (the tRNA molecule and the anticodon remain unaltered).
Which of the following is likely to be true?
A. Alanine would be incorporated into the peptide in place of cysteine.
B. Cysteine would continue to be brought to the ribosome by this tRNA.
C. Transcription would stop when this tRNA molecule entered the ribosome.
D. The amino acid bound to this tRNA would not be added to the growing polypeptide.
E. The result would differ in prokaryotes and eukaryotes.
There are differences in the amino acid sequence of rabbit and frog haemoglobin polypeptides. If mRNA for
rabbit haemoglobin is extracted from rabbit red blood cells, and is then placed in frog eggs, the cells will
produce rabbit haemoglobin polypeptides. This shows that
A. rabbit haemoglobin mRNA is the same as frog haemoglobin mRNA
B. the genetic code and the machinery of translation are substantially the same in widelydifferent organisms
C. the gene for haemoglobin is identical in all organisms
D. the DNA for rabbit hemoglobin is reverse transcribed into DNA in the frog eggs
E. frog ribosomes are incapable of binding to mammalian RNA
The repressor protein of the lac operon has two different recognition and binding sites for other molecules.
Which of the following pairs of molecules do you think it likely that these sites would bind?
A. RNA polymerase and lactose
B. RNA polymerase and DNA
C. a DNA sequence on the operator and lactose
D. a DNA sequence on the regulator gene and lactose
E. lactose and DNA polymerase
In the presence of high cellular concentrations of tryptophan
A. the repressor attaches to the DNA, but transcription proceeds
B. the repressor binds to tryptophan and then leaves the operator
C. tryptophan binds to the operator and prevents transcription
D. tryptophan binds to the repressor, which than binds to the operator
E. tryptophan binds to the repressor, which binds to the promoter and prevents transcription
Which of the following is true with respect to the lac operon?
A. The repressor only binds to the operator when it is bound to the product of the enzymes
coded for by the genes of the operon.
B. The repressor only binds to the operator when it is bound to the mRNA transcript of the
lacZ and lacY genes.
C. The repressor only leaves the operator when it is bound to the protein product of the lacI
gene.
D. The repressor is always bound to the operator, but changes shape when lactose binds to it,
allowing RNA polymerase to pass.
E. The repressor is bound to the operator, except when it is bound to the inducer.
The 'one gene: one enzyme' hypothesis had to be refined because
A. some genes code for lipids and carbohydrates
____ 41.
____ 42.
____ 43.
____ 44.
____ 45.
____ 46.
____ 47.
____ 48.
B. some genes code for many enzymes
C. some genes code for structural protein
D. some genes are transcribed and translated into other genes
E. some genes consist of protein
If you were shown an electron micrograph of a cell in which mRNA was being translated while it was still
being transcribed from the DNA, you would know
A. the gene product was in high demand at the point in the cell cycle at which the image was
captured
B. the cell was prokaryotic
C. transcription was occurring extremely fast
D. the electron micrograph showed the nucleus of the cell
E. the cell was eukaryotic
Which of the following is not true of prokaryotic cells?
A. There are no introns.
B. The methionine that enters the 'P' site at the beginning of translation has a formyl group
attached to it.
C. At least some of the genes are organized into operons.
D. The ribosomes, which are smaller than those in eukaryotes, bind to the 5' cap of the
mRNA.
E. he genome is circular.
It is thought possible that the evolution of modern eukaryotic cells involved an endosymbiotic relationship
between the prokaryotic cell ancestral to mitochondria and a host prokaryotic cell. Which of the following is
not true?
A. Mitochondria have DNA organized into a few tiny chromosomes held in a mini-nucleus.
B. The sequence of the DNA of mitochondria is similar to that of bacterial DNA.
C. Mitochondria divide by fission.
D. The prokaryotes ancestral to mitochondria may have had compartmentalized organelles.
E. Mitochondria have replication, transcription, and translation systems distinct from those of
the host cell.
Which of the following is not accurate?
A. The DNA in eukaryotes is arranged into chromosomes.
B. The DNA in eukaryotes contains noncoding regions.
C. The mRNA transcript of the DNA of eukaryotes has a 5' cap.
D. The ribosomes of eukaryotes are larger than in prokaryotes.
E. The spliceosomes are larger in eukaryotes than in prokaryotes.
Which of the following is not an example of noncoding DNA?
A. VNTRs
D. SINES
B. telomeres
E. histones
C. LINES
Mutations can be inheritable if they effect cells in the
A. placenta
D. testes
B. fallopian tubes
E. skin
C. prostate
The 'Central Dogma' states that the flow of genetic information is in the direction
A. protein, RNA, protein
D. RNA, DNA, protein
B. RNA, DNA, RNA
E. DNA, RNA, protein
C. protein, RNA, DNA
Which of the following statements is inaccurate concerning the deoxyribose sugar in a DNA nucleotide?
A. It has an oxygen atom attached to its 2' carbon.
____ 49.
____ 50.
____ 51.
____ 52.
B. It has an oxygen atom attached to its 3' carbon.
C. It has a base attached to its 1' carbon.
D. It has an oxygen atom attached to its 5' carbon.
E. It is found in chloroplasts and mitochondria.
There are three kinds of RNA polymerase in eukaryotes—RNA polymerases I, II, and III. RNA polymerases
I, II, and III are used, respectively, to transcribe
A. mRNA, tRNA, rRNA
D. tRNA, rRNA, mRNA
B. tRNA, mRNA, rRNA
E. all transcribe mRNA
C. rRNA, mRNA, tRNA
The operator of the lac operon is 'upstream' of the genes, which codes for enzymes. 'Upstream' means
A. the operator is in the first part of the lacZ gene
B. the operator is crossed by RNA polymerase before RNA polymerase reaches the genes,
which code for enzymes
C. the operator is crossed by RNA polymerase before RNA polymerase crosses the promoter
D. the operator is separated from the lacZ gene by thousands of bases
E. an intron separates the operator and the genes, which code for enzymes
The function of the polyadenine tail that is added to mRNA in eukaryotic cells is to
A. prevent degradation of the mRNA
B. initiate the binding of the mRNA to the ribosome
C. help the mRNA to bind to a pore in the nuclear membrane
D. add a specific amino acid sequence to the polypeptide produced
E. act as a signal for the termination of translation
A certain protein needs to have a high energy phosphate group added to it in the cytoplasm before it becomes
active. This offers the possibility of control at which of the following levels?
A. transcriptional
D. translational
B. operational
E. posttranslational
C. post-transcriptional
Matching
Match each item with the correct statement below.
A. template strand
I.
B. ligase
J.
C. primase
K.
D. DNA polymerase I
L.
E. lagging strand
M.
F. replication fork
N.
G. semi-conservative replication
O.
H. Okazaki fragment
single-stranded binding proteins
leading strand
gyrase
helicase
annealing
mitosis
DNA polymerase III
____ 53. process which results in each new DNA molecule consisting of one parental strand and one newly synthesized
strand
____ 54. unwinds DNA
____ 55. removes RNA primers
____ 56. new DNA strand synthesized in fragments
____ 57. division of a nucleus to form two daughter nuclei
____ 58. short lengths of DNA produced during synthesis of lagging strand
____ 59. keep newly separated strands of DNA apart
____ 60. new DNA strand which is synthesized continuously
____
____
____
____
____
____
____
61.
62.
63.
64.
65.
66.
67.
links sugars and phosphates together
area where DNA polymerase is bound to unwound DNA
DNA strand which directs synthesis of a complementary strand
builds RNA primers
relieves tension in DNA during unwinding
pairing of complementary strands of DNA due to hydrogen bonding
responsible for building new DNA strands during replication
Short Answer
68. Explain why DNA replication is slightly slower in the lagging strand of DNA than in the leading strand.
69. Hershey and Chase infected bacteria with bacteriophage which contained either protein labelled with 35S or
DNA labelled with 32P. Time for the infection process was allowed, then the cells were treated in a blender in
order to remove the bacteriophage cases from the surface of the bacterial cells and the bacteria and the
bacteriophage cases were recovered separately. It was found that the labelled DNA remained inside the
bacterial cells, indicating that DNA was the hereditary material injected by the bacteriophage into the cell to
direct the synthesis of new bacteriophage. The labelled protein was recovered with the bacteriophage cases,
and thus had never entered the bacteria. How would the results have differed if the step in which the cells
were put in the blender was omitted?
70. Imagine that you are a geneticist and are investigating a species of bacteriophage about which little is known.
How might Hershey and Chase's experiment be modified to discover whether the nucleic acid in the
bacteriophage is DNA or RNA?
71. Briefly describe the function of transfer RNA.
72. What is the amino acid sequence of the peptide that would be synthesized after transcription and translation of
the following piece of template strand DNA? You should note that the template strand of the DNA and the
newly-synthesized mRNA strand will be 'anti-parallel' (i.e., their 5' ends will be at opposite ends of the
strands of nucleic acid.)
5'
3'
_____________________
TCATGCGCAACA
codon
AGU
ACG
CGU
UGU
UGC
GCA
UGA
codon translations
amino acid
Ser
Thr
Arg
Cys
Cys
Ala
stop
73. Explain why it is likely that both DNA and RNA would be found in the nucleus of a eukaryotic cell.
74. Initial reluctance among the scientific community to accept that DNA was the molecule forming genes
(carrying a great deal of information) stemmed to some extent from the knowledge that DNA was a relatively
simple molecule, made up of only four nucleotides—adenine, cytosine, guanine, and thymine. Briefly explain
how DNA is capable of encoding a great deal of information, in spite of its apparently simple structure.
75. The diagram below represents the arginine synthesis pathway in the fungus Neurospora crassa.
precursor 
ornithine 
citrulline 
arginosuccinate 
arginine
enzyme A
argE gene
enzyme A
argF gene
enzyme C
argG gene
enzyme D
rgH gene
Suppose it was discovered that a strain of this fungus, when grown in minimal medium, accumulated
arginosuccinate in the medium, but was nonetheless capable of some growth. Propose several alternate
hypotheses that might account for this situation.
76. DNA 'fingerprinting' techniques that seek to compare samples of DNA with great accuracy, usually
concentrate on the comparison of VNTR DNA in the samples rather than the DNA found in the genes.
Explain why you think this is so.
77. In the century leading up to 1953, a long process occurred that resulted in the identification of DNA as the
hereditary material in cells and in the clarification of its structure. Show how a series of scientists built upon,
and extended the work of, their predecessors during this period.
t
Answer Section
MULTIPLE CHOICE
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
34.
35.
36.
37.
38.
39.
40.
41.
D
A
A
C
E
B
A
D
C
E
D
B
C
C
D
D
B
A
D
D
A
C
B
C
D
D
E
B
A
C
D
A
D
E
A
B
C
D
E
C
B
42.
43.
44.
45.
46.
47.
48.
49.
50.
51.
52.
D
A
E
E
D
E
A
C
B
A
E
MATCHING
53.
54.
55.
56.
57.
58.
59.
60.
61.
62.
63.
64.
65.
66.
67.
G
L
D
E
N
H
I
J
B
F
A
C
K
M
O
SHORT ANSWER
68. After it is initiated with the help of an RNA primer, synthesis of the new DNA can be continuous in the
leading strand in the direction followed by the replication fork. This is because replication is proceeding in a
5' - 3' direction - the only direction in which DNA polymerase III can synthesize a new strand of DNA. With
respect to the lagging strand, a number of primers are progressively attached to the parental strand and each
initiates the synthesis of a short Okazaki fragment in the direction opposite to that followed by the replication
fork, since only in this way can DNA polymerase III work in a 5' - 3' direction. Each of these primers has to
be removed by DNA polymerase I, which also replaces them with the appropriate nucleotides. DNA ligase
then joins the Okazaki fragments. All of these additional operations take time.
69. The bacteriophage cases would not have been shaken free of the bacteria and both the labelled protein and the
labelled DNA would have been recovered with the bacterial cells. It would, therefore, have been impossible to
reach any conclusions regarding whether DNA or protein was the hereditary material injected by the
bacteriophage into the cells.
70. - You might grow the bacteriophage in a medium containing radioactive uracil. If the nucleic acid is RNA,
the radioactivity would be found in the bacteria after infection and blending. If the bacteriophage contains
DNA, no radioactivity would be found in the bacteria.
71.
72.
73.
74.
75.
76.
- You might grow the bacteriophage in a medium containing radioactive thymine. If the nucleic acid is DNA,
the radioactivity would be found in the bacteria after infection and blending. If the 'phage contains RNA, no
radioactivity would be found in the bacteria.
- To interact with ribosomes, amino acids and mRNA during protein synthesis.
- To act as an interface, matching specific amino acids to specific codons in the mRNA.
- To ensure that amino acids are added to the growing polypeptide chain in the correct sequence.
Cys - Cys - Ala
- DNA is incorporated into chromosomes and never leaves the nucleus.
- mRNA is present in the nucleus as it is being transcribed from DNA.
- rRNA is present in the nucleus as a component of ribosomes, which are assembled in the nucleolus.
Groups of nucleotides encode information. If a group consists of more than one nucleotide, the number of
possible combinations (or 'codewords') is large.
- A mutation in the argG gene that resulted in a version of enzyme C having greater than normal activity.
- A mutation in the argH gene that resulted in a version of enzyme D having lower than normal activity.
- Defects in the regulatory mechanisms governing the rates of expression of genes argG and argH.
The characteristics of VNTR microsatellites (the DNA of which is non-coding) differ widely between
different individuals. On the other hand, because variation in base sequence often has such destructive effects
on the functional ability of the protein coded for, the sequence of bases in the DNA of genes is often highly
conserved and there may be only a few versions of a gene throughout the human population. If your purpose
is to demonstrate that it is unlikely that two samples of DNA are identical by chance, it is best to work with
DNA that would normally be expected to vary widely between individuals.
ESSAY
77. - Miescher demonstrated that "nuclein" was present in the nucleus.
- Hammerling showed that it was very likely that the hereditary material resided in the nucleus.
- Griffith demonstrated that a molecule, which could be extracted from dead bacteria, could transform live
bacteria and transfer hereditary information to the bacteria. If this material could be identified, the chemical
nature of the hereditary material would be known.
- Avery, McCarty, and Macleod identified DNA as the molecule that transforms bacteria.
- Hershey and Chase confirmed that DNA was the hereditary material—this time using bacteriophage.
- Chargaff provided the first evidence indicating that bases might be paired in DNA.
- Franklin generated X-ray diffraction data that suggested that DNA was a helical molecule.
- Watson and Crick produced the double helix model with inward-pointing paired hydrogen-bonded bases,
which explained Chargaff's data and conformed with the dimensions of Franklin's image.